We describe first results from an updated X-ray
nonequilibrium-ionization code using as a dynamical substrate a
Sedov-Taylor blast wave appropriate for a supernova remnant (SNR).
The code has extensively updated atomic physics, particularly in iron
L-shell transitions, and allows an arbitrary ratio \beta of
postshock electron temperature T_e to ion temperature T_i, to
describe possible nonthermal plasma heating processes in the shock
wave. We show that at the resolution of the ASCA X-ray satellite, our
calculated models are poorly fit by simple models in the XSPEC
data-reduction package, such as constant-temperature
nonequilibrium-ionization ``neq'' models with a single ionization
timescale. Models with the same postshock electron temperature but
varying ion temperatures (i.e., varying \beta with constant \beta
T_i) produce quite different high-energy continua and should be
distinguishable in practice, holding out the possibility of measuring
the extent of plasma heating. We show that a simple multi-zone model
superposing several ``neq'' models with different temperatures and
with ionization timescales chosen appropriately can provide a much
better fit to our full simulations, and the fitted temperatures
accurately reflect the mass-weighted temperature of our full Sedov
model. We plan to adapt our models for use in XSPEC, and make them
available to the general astronomical community.